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sched/fair: Properly deactivate sched_delayed task upon class change

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__sched_setscheduler() goes through an enqueue/dequeue cycle like so:

  flags := DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
  prev_class->dequeue_task(rq, p, flags);
  new_class->enqueue_task(rq, p, flags);

when prev_class := fair_sched_class, this is followed by:

  dequeue_task(rq, p, DEQUEUE_NOCLOCK | DEQUEUE_SLEEP);

the idea being that since the task has switched classes, we need to drop
the sched_delayed logic and have that task be deactivated per its previous
dequeue_task(..., DEQUEUE_SLEEP).

Unfortunately, this leaves the task on_rq. This is missing the tail end of
dequeue_entities() that issues __block_task(), which __sched_setscheduler()
won't have done due to not using DEQUEUE_DELAYED - not that it should, as
it is pretty much a fair_sched_class specific thing.

Make switched_from_fair() properly deactivate sched_delayed tasks upon
class changes via __block_task(), as if a
  dequeue_task(..., DEQUEUE_DELAYED)
had been issued.

Fixes: 2e0199df25 ("sched/fair: Prepare exit/cleanup paths for delayed_dequeue")
Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
Reported-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20240829135353.1524260-1-vschneid@redhat.com
This commit is contained in:
Valentin Schneider 2024-08-29 15:53:53 +02:00 committed by Peter Zijlstra
parent 9c602adb79
commit 75b6499024
1 changed files with 17 additions and 8 deletions
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25
kernel/sched/fair.c
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@ -5456,6 +5456,13 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
static inline void finish_delayed_dequeue_entity(struct sched_entity *se)
{
se->sched_delayed = 0;
if (sched_feat(DELAY_ZERO) && se->vlag > 0)
se->vlag = 0;
}
static bool
dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
@ -5531,11 +5538,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) != DEQUEUE_SAVE)
update_min_vruntime(cfs_rq);
if (flags & DEQUEUE_DELAYED) {
se->sched_delayed = 0;
if (sched_feat(DELAY_ZERO) && se->vlag > 0)
se->vlag = 0;
}
if (flags & DEQUEUE_DELAYED)
finish_delayed_dequeue_entity(se);
if (cfs_rq->nr_running == 0)
update_idle_cfs_rq_clock_pelt(cfs_rq);
@ -13107,11 +13111,16 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
* and we cannot use DEQUEUE_DELAYED.
*/
if (p->se.sched_delayed) {
/* First, dequeue it from its new class' structures */
dequeue_task(rq, p, DEQUEUE_NOCLOCK | DEQUEUE_SLEEP);
p->se.sched_delayed = 0;
/*
* Now, clean up the fair_sched_class side of things
* related to sched_delayed being true and that wasn't done
* due to the generic dequeue not using DEQUEUE_DELAYED.
*/
finish_delayed_dequeue_entity(&p->se);
p->se.rel_deadline = 0;
if (sched_feat(DELAY_ZERO) && p->se.vlag > 0)
p->se.vlag = 0;
__block_task(rq, p);
}
}